The present invention relates to a control apparatus for controlling the operation of a marine engine. More particularly, it relates to such an engine control apparatus which is effective to suppress variations in the output power of the engine when a boat having the engine mounted thereon is trolling.
FIG. 7 schematically illustrates a typical example of an outboard marine engine 1 mounted on a boat 3 at a location outside a boat hull 3a In this figure, the engine 1 in the form of an internal combustion engine for outboard use is disposed outside the boat hull 3a at the stern thereof and mounted to the boat hull 3a through a mounting member la. A propulsion screw 2 is disposed under water and operatively connected with the engine 1 so that it is thereby driven to rotate.
FIG. 8 shows in block form the general construction of a conventional engine control apparatus for controlling the outboard engine 1 of FIG. 7. In this figure, a rotational speed sensor 4 is mounted on a camshaft or crankshaft (not illustrated) of the engine 1 so that it generates a crank signal representative of a reference crankshaft position in synchronization with the rotation of the unillustrated crankshaft for sensing the rotational speed or the number of revolutions per minutes of the engine 1 and generating a corresponding output signal R. A throttle sensor 5 senses the throttle opening or the degree of opening of a throttle valve (not shown) of the engine 1 corresponding to the quantity of depression of an unillustrated accelerator pedal of the engine 1 by an operator, and generates a corresponding throttle signal a. A gear position sensor 8 senses the gear position of a transmission (not shown) of the engine 1 and generates a corresponding gear position signal G. A controller 6 receives output signals from various sensors indicative of various engine operating conditions including the output signals R, a, G of the rotational speed sensor 4, the throttle sensor 5 and the gear position sensor 8, and generates a drive signal A for controlling various engine control parameters on the basis of these output signals. An actuator means 7 is operatively connected to the controller 6 so that it is driven to operate by means of the drive signal A from the controller 6. The actuator means 7 controls various driving and control elements or devices such as a fuel pump, an ignition coil, a throttle actuator, a starter motor and the like associated with the engine 1.
Next, the operation of the above-described conventional engine control apparatus will be described in detail while referring to FIGS. 7 and 8. First, the controller 6 generates a drive signal A based on the output signals from the various sensors including the rotational speed signal R, the throttle signal .alpha., the gear position signal G, the reference crank signal and the like representative of various engine operating conditions, for controlling the actuator means 7 (e.g., for controlling a fuel pump, an ignition coil, a throttle valve, etc.) as well as calculating and controlling operational timings thereof such as fuel supply or injection timing, ignition timing, etc.
Here, it should be noted that in the case of the marine engine 1, the boat should be caused to travel at a low speed during trolling. However, since in this case, the engine 1 is controlled in a feedback manner so as to make the air/fuel ratio of the mixture to be at a stoichiometric value (i.e., 14.7), as in the case of cruising, engine hunting often results, causing substantial variations in the travelling speed of the boat 3 and resultant discomfort to the passengers therein.
In addition, the controller 6 receives an output signal from an unillustrated pressure senor which senses an intake manifold pressure or an intake air pressure representative of an engine load, and averages it with a predetermined averaging coefficient to provide an averaged value which is regarded as the engine load at that time. Based on the thus averaged intake manifold pressure, the controller 6 properly adjusts engine control parameters. That is, the pressure of intake air in an intake manifold normally varies with high frequencies on each intake stroke of each cylinder, so averaging of the intake manifold pressure is required to stabilize its value in order to utilize it for engine control.
In this case, during trolling in which the boat 3 is caused to travel in a low speed, the period of a pulsating component of the intake manifold pressure tends to become longer with respect to the averaging coefficient, so usual averaging becomes insufficient. As a result, the pulsating component reflected on the engine control parameters to cause variations in the rotational speed of the engine, thus substantially impairing riding comfort.